The peripheral nervous system originates from two main cell classes: neural crest and cranial ectodermal placodes. Placodes are discrete regions of thickened epithelial that give rise to portions of the cranial sensory ganglia as well as form the paired sense organs (lens, nose, ears). Some of the cranial sensory ganglia arise solely from placodes (e.g. acoustic ganglion from otic placode), whereas others are derived from both placodes and neural crest (e.g. trigeminal placode). Placodes and neural crest share several properties including the ability to migrate and the ability to undergo an epithelial to mesenchymal transition. Their progeny are also similar: sensory neurons, glia, neuroendocrine cells, and cells that can secrete special extracellular matrices. Although the mechanisms involved in neural crest induction, migration, and differentiation have been explored extensively, placode development has not. In this proposal the following experiments are described to clarify the relationship between neural crest and placodes in the developing chicken embryo: test if tissue interactions necessary for neural crest induction will induce placodes in the developing chicken embryo: test if tissue interactions necessary for neural crest induction will induce placodes, what molecules are necessary for placode induction, and to determine if neural crest and placodes share a common lineage by fate mapping. These proposed experiments will extend our understanding of very early events in the development of the peripheral nervous system in vertebrates as well as shed light on human craniofacial malformations in which placode formation is disrupted.